420/44 DB Owners Club

RBB · May 24, 2023

NorCalRobert said:
Did WOT change from.old props to the new ones?
I had my props worked and went from the factory 24x27 Medium cup to a light cup and went from WOT of 2645 to 2680 which is now in the range recommended for the Cummins QSC motor

My Rpm’s stayed the same.

RBB · May 24, 2023

NorCalRobert said:
Did WOT change from.old props to the new ones?
I had my props worked and went from the factory 24x27 Medium cup to a light cup and went from WOT of 2645 to 2680 which is now in the range recommended for the Cummins QSC motor

What speed are you running before and after sorry my wot maybe 2730 rpm’s at 30.3 SOG

NorCalRobert · May 25, 2023

RBB said:
What speed are you running before and after sorry my wot maybe 2730 rpm’s at 30.3 SOG

2730 is high, if memory is correct 32
Her is the chart from Seaboard marine https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

NorCalRobert · May 25, 2023

RBB said:
Our 2006 qsc 500 44db turns 2680 rpm at wot.
Does that sound right?

This is the correct rpm range for the Cummins QSC
See chart https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

RBB · May 25, 2023

NorCalRobert said:
This is the correct rpm range for the Cummins QSC
See chart https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

So maybe they need some cup?

NorCalRobert · May 25, 2023

RBB said:
My Rpm’s stayed the same.

One more thing, when I had my props redone from 24x27 M-cup props to 24x27 Light cup props I went from planing cruise of 2275-2280rpm and now I need to hit 2300rpm before it planes.
Here are a few screen shots of before and after the prop work.
The 2289rpm is with M-cup props at 25.7mph and the 2307rpm is with the new Light cup props and 23.1mph
Note: I do MPH not knots

RBB · May 25, 2023

My other set of props the boat was faster.
Do you run here at 2300 rpm on a all day cruise?

NorCalRobert · May 25, 2023

RBB said:
View attachment 145014 My other set of props the boat was faster.
Do you run here at 2300 rpm on an all day cruise?

Yes hours at a time.

NorCalRobert · May 25, 2023

RBB said:
View attachment 145014 My other set of props the boat was faster.
Do you run here at 2300 rpm on a all day cruise?

If WOT is 2665rpm with old props then you are in the optimum range for longevity of you QSC motors, 2730 is too high although it is less load on the motors which is good too but your loss of speed is more
https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

RBB · May 25, 2023

NorCalRobert said:
If WOT is 2665rpm with old props then you are in the optimum range for longevity of you QSC motors, 2730 is too high although it is less load on the motors which is good too but your loss of speed is more
https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

I just talked to a prop guy and he said I need alittle cup. If I can get her on the hard I am going to change my props out , back to my original ones and have my new ones cupped alittle.

NorCalRobert · May 25, 2023

RBB said:
I just talked to a prop guy and he said I need alittle cup. If I can get her on the hard I am going to change my props out , back to my original ones and have my new ones cupped alittle.

If you carry full water and full fuel along with all the other little spares etc the factory 24x27 M-cup is just a bit to much on mine and went to the light cupping. Info should be stamped on your props.

RBB · May 25, 2023

The props I took off r m cup. Not sure what I put on it, but this was on the box

NorCalRobert · May 25, 2023

RBB said:
View attachment 145020 View attachment 145021 View attachment 145022 View attachment 145023 View attachment 145017 The props I took off r m cup. Not sure what I put on it, but this was on the boxView attachment 145017

I wonder if those have no cupping since nothing is stated on the box

Mark.60 · May 25, 2023

If you look at the charts from sea board marine Tony Athens talks about the more critical part of proper propping.
Fuel burn at different rpms

RBB · May 26, 2023

NorCalRobert said:
I wonder if those have no cupping since nothing is stated on the box

That’s what I am thinking, no cup. I gonna swap them back out with my originals that got redone.

Irie308 · May 30, 2023

I seem to trip the GFI in the forward head whenever I switch between shore or gen power. Hopping it’s just a bad gfi outlet. Anything else I should check?

Bruce SEA 993 · May 30, 2023

GFCI receptacles do not last forever. The surge, as small as it is when you flip the switch could be enough to trip it.

Super easy to change out the GFCI as a test. Do not forget to turn off the breaker!!!

Let us know if you find a cause.

AEO · May 30, 2023

Does anyone know if there any rules or cautions with the keys in the ‘ON’ position?

Just wondering if they have a time limit if left in ON when engines not running.

Bruce SEA 993 · May 30, 2023

I wonder the same thing. I think it just powers up the helm items.

Curious, what does your accessory DC switch control on your STBD side?

Cheers!

Irie308 · May 30, 2023

Not sure they matter other than the fact you can accidentally start from helm. Not likely but it could happen…heck I’ve accidentally laid on the horn. My rule is at anchor I leave the keys on in case I need to get out of dodge in a hurry. At the dock they are off.

420/44 DB Owners Club

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Attachments

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Active Member

Well-Known Member

Well-Known Member

Forum statistics